Non-linear optical properties, electrical conductivity and semiconductivity of organic semiconductor compounds have received attention in the organic electronics and optoelectronics fields and the development of various devices has been advanced actively. Typical examples of organic semiconductor compounds include phthalocyanine compounds, porphyrin compounds and polyacenes. Properties such as non-linear optical properties, electrical conductivity and semiconductivity, which are required for using these compounds as organic materials to form devices, largely depend on crystallinity and orientation other than only purity of each of the materials.
However, it was difficult to highly purify these materials due to the reason that many compounds with extended π-conjugated systems are insoluble in solvents and susceptible to oxidation in air. In addition, a large-scale apparatus has been required for forming films, for example, vacuum deposition has been performed to obtain crystallized films with high orientation. In recent years, organic field effect transistor (FET) devices using organic semiconductor compounds as the semiconductor layers have received attention. Organic semiconductor compounds, which show more flexible film properties than in organic materials such as silicon, have been regarded as suitable materials for producing flexible devices using plastics as substrates.
However, as described above, phthalocyanine compounds, porphyrin compounds, pentacene and the like that are typical examples of organic semiconductor compounds are hardly soluble in solvents, so the formation of their films on substrates has only been possible by vacuum deposition. Therefore, they have disadvantages in that complicated vacuum deposition apparatuses are necessary; substrate materials are limited because the substrate temperature must be maintained at high temperatures; and the like. On the other hand, FETs are fabricated more easily by forming thin films by spin coating or the like from a solution of organic semiconductors soluble in organic solvents. As an example of the above, π-conjugated polymers are used for semiconductor layers (Japan Society of Applied Physics, “Japanese Journal of Applied Physics,” Vol. 30, pp. L610-L611, 1991). However, an organic FET of this type generally has a low mobility and improvement of the properties is expected.
In order to improve the above disadvantages, there is also reported a FET using a film in which a soluble precursor thin film of pentacene is formed by coating and transformed to pentacene by heat-treatment (WILLEY-VCH Verlag GmbH, “Advanced Materials,” Vol. 11, p. 480-483, 1999).
In this case, the conversion to pentacene by a reverse Diels-Alder reaction has required a high-temperature treatment of 170° C. or more. Further, conversion to pentacene at a low temperature is also reported (American Chemical Society, “Journal of American Chemical Society,” Vol. 124, p. 8812-8813, 2002), but there was a problem in the stability of a soluble precursor of pentacene.